Halogenated polymer compositions containing a metal compound stabilizer and a coated acid absorber costabilizer

ABSTRACT

Vinyl halide resin compositions containing a metal compound stabilizer and coated acid absorber particles, where the coating consists of a tin-based coating or a complex calcium/zinc/strontium phosphate-based coating, are used to confer heat stability to such compositions. Use of the costabilizers of this invention results in economic advantages and material cost savings.

This application is a Division of Ser. No. 09/360,277 filed Jul. 26,1999.

TECHNICAL FIELD OF THE INVENTION

This invention relates to heat stabilizers for halogenated polymers suchas polyvinyl chloride (PVC) containing a primary metal stabilizer and acoated acid absorber as costabilizer. The acid absorber costabilizerparticles of about submicron to about 10 microns in size are coated witha tin-based coating or a complex calcium/zinc/strontium phosphate-basedcoating.

BACKGROUND OF THE INVENTION

It is well known that halogenated polymers such as PVC may be heatstabilized by combinations of divalent metal carboxylates andhydrotalcite-like acid absorbers or scavengers. U.S. Pat. Nos. 4,221,687and 5,084,499 are examples of patents disclosing such stabilizers. It isalso known to stabilize vinyl halide resin compositions with mixed metalstabilizers, hydrotalcite and a dialkyltin oxide as disclosed in U.S.Pat. No. 5,561,182. Acid acceptors such as hydrotalcite and zeolite havestabilizer value in PVC and other halogenated polymers. In polymericmatrices, these additives have very little stabilizing effect and are atbest secondary stabilizers.

It has been suggested that acid absorbers which are effective asstabilizers form addition complexes at degrading sites, tending todeactivate such sites and to capture catalytic, highly mobile HCI beforeelimination of further HCI can occur. These stabilizers are believed tohave coordinating properties that enable their being at the right placeat the right time, at least to a far greater extent than common,acid-reactive fillers.

When used as a primary stabilizer, additives such as hydrotalcite andzeolite (and certain others) provide stability comparable to, forexample, barium stearate. In other words, process stability is long, butcolor hold is poor. This has been corrected in practice by combiningthese additives with zinc carboxylates. The effect has been to treat theacid absorber as if it were a barium or calcium component of a mixedmetal stabilizer. Acid absorber particles coated with zinc carboxylatesare useful in flexible PVC compositions where the application has rathermodest stabilizer demand, for example, cove base extrusion. These coatedacid absorbers are also costabilizers for organotin mercaptides in rigidPVC, and are widely available.

Zeolite or hydrotalcite particles coated with zinc carboxylates arerelatively ineffective as costabilizers in a number of significantinstances. For instance, in concert with lead stabilizers in flexiblePVC, part of the lead stabilizer content may be replaced with such acostabilizer without significant loss of dynamic stability, but with nogain. Since lead stabilizers are highly cost effective, such replacementis of little value. In rigid PVC, partial replacement of lead stabilizerwith zinc coated zeolite or hydrotalcite is strongly detrimental todynamic stability. With "reverse ester" organotins, contrary to thebehavior with dialkyltin thioglycolates, zinc coated zeolite orhydrotalcite is almost totally ineffective as a costabilizer withdialkyltin beta-mercaptooleates in rigid PVC compositions. Furthermore,zinc coated zeolite or hydrotalcite is largely ineffective as acostabilizer with organotin carboxylates such as dialkyltin maleates ormaleate half esters. In highly filled flexible PVC compositions, such asfloor tile, no advantage is found by employing zinc carboxylate coatedacid absorbers.

It is believed likely that the zinc carboxylate coating of acid absorberparticles functions as a phase transfer catalyst, thereby enabling closecoordination to a potential degrading site. However, due to theineffectiveness of a zinc coated zeolite or hydrotalcite in a number ofinstances as outlined above, alternative phase transfer catalysts orcostabilizers are needed.

SUMMARY OF THE INVENTION

This invention is directed to vinyl halide resin compositions containinga metal compound stabilizer and coated acid absorber particles where thecoating consists of a tin-based coating or a complexcalcium/zinc/strontium phosphate-based coating to confer heat stabilityto such compositions.

It has been found that the addition of a tin-based coating to acidabsorber particles, such as zeolite and hydrotalcite, enable theirperformance as costabilizers with economic advantage. For example,zeolite and hydrotalcite particles coated with a dialkyltin oxide and afatty acid have been found particularly effective with organotincarboxylates as dynamic heat stabilizers. There is also the advantage ofmaterial cost savings in partial replacement of the organotincarboxylate with the costabilizer. With reverse ester tins, while theremay be little economic advantage in partial replacement with the coatedacid absorbers of this invention, the compositions of this inventionhave been found to provide improved dynamic stability.

In the case of lead stabilzers, acid absorber particles having a complexcalcium/zinc/strontium phosphate-based coating have been developed whichpermit partial replacement of the lead stabilizers with improved dynamicstability. For example, in highly flame retardant, low smokecompositions, the complex coated particles act as a costabilizer withthe lead stabilizer to provide improved dynamic stability. Thesecompositions are particularly suitable where the reduction of leadstabilizer is also desired. Furthermore, in flexible PVC compositionsfor high speed, thin mold extrusion of wire insulation, when it isdesirable to use Pb/Ba stearate as a stabilizer, the complexcalcium/zinc/strontium phosphate-based coated zeolite particles enablethe partial replacement of Pb/Ba stearate with improved stabilizingeffectiveness.

DETAILED DESCRIPTION OF THE INVENTION

A. Vinyl Halide Resin

The vinyl halide resin employed is most commonly a homopolymer of vinylchloride, i.e., polyvinyl chloride. It is to be understood, however,that this invention is not limited to a particular vinyl halide resinsuch as polyvinyl chloride or its copolymers. Other halogen-containingresins which are employed and which illustrate the principles of thisinvention include chlorinated polyethylene, chlorosulfonatedpolyethylene, chlorinated polyvinyl chloride, and other vinyl halideresin types. Vinyl halide resin, as understood herein, and asappreciated in the art, is a common term and is adopted to define thoseresins or polymers usually derived by polymerization or copolymerizationof vinyl monomers including vinyl chloride with or without othercomonomers including vinyl chloride with or without other comonomerssuch as ethylene, propylene, vinyl acetate, vinyl ethers, vinylidenechloride, methacrylate, acrylates, styrene, etc. A simple case is theconversion of vinyl chloride H₂ C--CHCI to polyvinyl chloride (CH₂CHCI--)n wherein the halogen is bonded to the carbon atoms of the carbonchain of the polymer. Other examples of such vinyl halide resins wouldinclude vinylidene chloride polymers, vinyl chloride-vinyl estercopolymers, vinyl chloride-vinyl ether copolymers, vinylchloride-vinylidene copolymers, vinyl chloride-propylene copolymers,chlorinate polyethylene, and the like. Of course, the vinyl halidecommonly used in the industry is the chloride, although others such asbromide and fluoride may be used. Examples of the latter polymersinclude polyvinyl bromide, polyvinyl fluoride, and copolymers thereof.

B. Stabilizer System

The coated acid absorbers of this invention are preferably zeolite orhydrotalcite particles coated with either a tin-based coating or acomplex calcium/zinc/strontium-based coating. In the case of thetin-based coating, a dialkyltin oxide or a dialkyltin sulfide and afatty acid are coated onto the zeolite or hydrotalcite particles. Thefatty acid is selected from the group consisting of stearic, oleic,octoic and lauric acids. The dialkyltin oxide is preferably a C₁ -C₈dialkyltin oxide such as dibutyl tin oxide and the fatty acid is mostpreferably stearic or lauric acid. The acid absorber particles range insize from submicron to about 10 microns. The particles usually compriseabout 90-99% by weight of zeolite or hydrotalcite with a coating in anamount of about 1-10% by weight. Other acid absorbers are well known andmay be used. The coating usually comprises about 2-5% by weight of thetin-based or complex metal-based component with the balance made up of afatty acid. The costabilizer is used in a range of about 0.2 to about 3to 4 phr based on 100 parts of PVC.

A calcium/strontium/zinc complex suitable for use is HALOX SZP-391 whichgenerically is identified as calcium strontium zinc phosphosilicatehaving a mean particle size of about 2 microns. The theoretical chemicalcomposition in percent by weight is typically 41.9% ZnO, 14.7% CaO, 4.5%SrO, 14.7% SiO₂, 17.7% P₂ O₅ and 5.5% L.O.I. (450° C.). These complexesare manufactured under U.S. Pat. Nos. 3,846,148 or 3,852,087 and thesedisclosures are incorporated herein by reference.

The coated acid absorber particles, such as zeolite and hydrotalcite,are coated by adding the particles either to a ribbon blender or sigmablade mixer. While the batch is rotating, the fatty acid and metal-basedingredients are metered in, generally over a period of several minutes.Blending is then maintained for 5-15 additional minutes prior todischarge. More intensive blenders, such as Henschel or Littlefordmixers, may also be used.

Metal compound heat stabilizers in vinyl halide resin. compositions arewell known. The metal compound stabilizer is normally used in an amountof about 0.5 to 5 parts of PVC. As developed in the background of thisinvention, these metal compounds serve to capture HCI liberated duringheat processing of the vinyl halide resin composition into its finalshape. Metal salts and mixed metal salts are employed as heatstabilizing compositions. The metal component can be a barium, cadmium,calcium, zinc, strontium, tin, lead, or antimony salt. Usually metalsalts of a carboxylic acid, advantageously of a C₈ -C₂₄ monocarboxylicacid, such as lauric, oleic, stearic, octoic, or similar fatty acidsalts are used. Salts of such acids, and their preparation, are familiarto those skilled in the art to which this present invention pertains.

The metal compound stabilizers with which the coated acid absorbercostabilizers are employed may be selected from a wide variety ofstabilizers. In particular, as stated above, reverse ester tins and tincarboxylates are employed with economic advantage and/or improveddynamic stability with the coated acid absorbers as costabilizers. Suchorganotin stabilizers comprise several classes of compounds. Thecommercial products include blends of dialkyltin bis(iso-thioglycolates)with monoalkyltin tris(iso-thioglycolates), referred to as "tinmercaptides." Similar blends of dialkyltin bis(2-mercaptoethyl oleates),referred to as "reverse ester tins" in the trade, are employed. Otherorganotin stabilizers include dialkytin carboxylate esters, of which themost common are dialkytin maleate esters such as dialkyltin maleateoctoate. Lead stabilizers such as lead stearate, barium stearate, andmixtures thereof, can be employed as the primary metal compoundstabilizer. Others include dibasic lead phthalate, tetrabasic leadfumarate, dibasic lead phosphite, and the like. Other antimony, barium,calcium, cadmium, zinc, lead, strontium, and tin metal compoundstabilizers may be employed in view of the teachings of this inventionas understood by a person of ordinary skill in the art in view of thedetailed description.

The following examples illustrate the practice of this invention. Theseexamples are not considered to be limiting upon the scope of theinvention.

A series of examples 1-5 were performed to illustrate the practice ofthe invention with zeolite acid absorber particles coated with stearicacid plus a complex calcium/zinc/strontium phosphate, identified above.

The test vinyl halide resin composition comprised the followingcomponents in parts per 100 parts resin (phr):

    ______________________________________                                        Geon 30 PVC          100                                                        Santicizer 2148 plasticizer 27                                                Great Lakes CP45 brominated 20                                                flame retardant                                                               Aluminum trihydrate 20                                                        Magnesium hydroxide 5                                                         Zinc borate 10                                                                Ammonium octamolybdate (AOM) 10                                               Antimony oxide 3                                                              Stearic acid 0.3                                                              Paraffin wax 0.3                                                            ______________________________________                                    

Santicizer 2148 is an "aryl alkyl phosphate" plasticizer supplied byMonsanto. CP45 is a proprietary polybrominated organic flame retardantfrom Great Lakes Chemical.

Dynamic stabilities of the Examples 1-5 compositions containing thestabilizers identified in the following Table 1 was determined using aBrabender PL-2000 Torque Rheometer using an electrically heated, Type 6,3-piece head. Samples were removed periodically with square, long-nosedpliers and failure times were at 200° C., 120 rpm with a 70 grams batch.Examples 4 and 5 employed "Halstab 1219" costabilizer to identify theinventive acid absorber particles (about 1-5 microns) of 95% zeolitecoated with 3% stearic acid plus 2% of a complex calcium/zinc/strontiumphosphate (HALOX 52P-391). Examples 4 and 5 containing Halstab 1219 farout performed Examples 1-3 which employed the lead metal stabilizersalone. Thus, Examples 1-5 illustrate the partial replacement of commonlead stabilizers with the inventive costabilizers thereby yieldingimproved dynamic stability. Furthermore, highly flame retardant, lowsmoke compositions as exemplified by Examples 1-5 may be formulatedwhere additives are needed for FR/LS (Flame Resistant/Low Smoke)properties without detracting from stability.

                  TABLE 1                                                         ______________________________________                                        Example                         Failure Time                                    No. Stabilizer phr (minutes)                                                ______________________________________                                        1         Dibasic lead phthalate                                                                        6     38                                              2 Dibasic lead phthalate 8 46                                                 3 Dibasic lead phthalate 6 54                                                  Tetrabasic lead fumarate 2                                                   4 Dibasic lead phthalate 6 82                                                  Halstab 1219 2                                                               5 Dibasic lead phthalate 4 101                                                 Dibasic lead phosphite 2                                                      Halstab 1219 2                                                             ______________________________________                                    

Examples 6-8 of Table 2 further illustrate the use of coated acidabsorbers as partial replacements for lead stabilizers. In these cases,a Pb/Ba stearate was employed as the primary stabilizer, and Examples7-8 used a partial substitution with Halstab 1219 which is the complexcoated costabilizer identified above. The flexible PVC compositions wereformulated for high speed, thin wall extrusion of wire insulation. Insuch cases it is desirable to use a Pb/Ba stearate as the stabilizerbecause of its combination of lubrication value and solubility in PVC ofboth the stabilizer and its primary reaction product, basic leadchloride. Stabilization effectiveness, however, is in itself notcomparable to, for example, dibasic lead phthalate. In these examples,the test compound comprised (phr):

    ______________________________________                                        Geon 30 PVC        100                                                          Ditridecyl Phthalate 30                                                       Tris-iso-nonyl trimellitate 20                                                CaCO.sub.3 5                                                                  Calcined clay 12                                                              Antimony oxide 2                                                            ______________________________________                                    

Dynamic stabilities were determined as in the foregoing examples and thefailure times were observed at 190° C., 100 rpm for a 65 grams batch, asnoted in the following Table 2. As demonstrated by Examples 6-8, thecoated acid absorber costabilizer of this invention may be substitutedfor lead stabilizers with significant improvements in heat stabilitiesand color hold.

                  TABLE 2                                                         ______________________________________                                        Example                         Failure Time                                    No. Stabilizer phr (minutes)                                                ______________________________________                                        6         Halstab BA-1    2     64                                               (Pb/Ba stearate)                                                             7 Halstab BA-1 1.5 >100                                                        Halstab 1219 0.5                                                             8 Halstab BA-1 1.3 >100+                                                       Dibasic lead phthalate 0.2 excellent                                          Halstab 1219 0.5 color hold                                                ______________________________________                                    

Examples 9-12 demonstrate the use of acid absorber particles as acostabilizer for reverse tins and tin carboxylates. "Halstab 1214"identifies the costabilizer which comprises 95% zeolite particles coatedwith 2% dibutyltin oxide and 3% stearic acid. The test compositionincluded the following components (phr):

    ______________________________________                                               Oxy 220 PVC                                                                             100                                                            CaCO.sub.3 20                                                                 Paraloid K334 6                                                               Paraloid K120N 1.2                                                            Paraloid K175 0.3                                                             Calcium Stearate 1.3                                                          Paraffin wax 1                                                                AC629A PE 0.2                                                                 Loxiol G33 0.3                                                              ______________________________________                                    

Paraloid K334 is an elastomeric acrylic impact modifier; K120N, aprocessing aid; and K-175, a lubricating processing aid, all from Rohm &Haas. AC629A is partly oxidized low MW polyethylene from Allied Signal,and Loxiol G-33, a complex ester lubricant from Henkel.

Morton TM 694 reverse ester tin is a proprietary blend of dimethyltinbis (2-mercapto-ethyl oleate) and monomethyltin tris (2-mercaptoethyloleate). Akcros T878M maleate ester is a proprietary half ester ofdibutyltin maleate laurate. They were employed as the primarystabilizers with Halstab 1214 costabilizer. With reference to Table 3for Examples 9-12, it has been demonstrated that the use of the coatedacid absorbers as costabilizers for reverse ester tins enables theirpartial replacement to provide improved dynamic stabilities. In the caseof the organotin carboxylate, there is also the advantage of materialcost savings with partial replacement by the costabilizer.

                  TABLE 3                                                         ______________________________________                                        Example                        Failure Time                                     No. Stabilizer phr (minutes)                                                ______________________________________                                         9         Morton TM694 2      31                                                reverse ester tin                                                            10 Morton TM694 1 44                                                           Halstab 1214 1                                                               11 Akcros T878M 2.5 27                                                         (maleate ester)                                                              12 Akcros T878M 1.25 38                                                        Halstab 1214 1                                                             ______________________________________                                    

Examples 13-16 were performed in order to determine the effect of thestabilizer and costabilizer in a pipe formulation as follows (phr):

    ______________________________________                                               PVC       100                                                            CaCO.sub.3 5                                                                  TiO.sub.2 1                                                                   Paraloid K120N 0.5                                                            Calcium stearate 0.5                                                          Paraffin wax 1.2                                                            ______________________________________                                    

Dynamic stabilities were again determined at 190° C., 60 rpm, for a 65grams batch, with the results reported in the following Table 4. FerroS1027 is antimony tris(isobutyl thioglycolate).

                  TABLE 4                                                         ______________________________________                                        Example                        Failure Time                                     No. Stabilizer phr (minutes)                                                ______________________________________                                        13         Morton TM694 0.4    17                                               14 Morton TM694 0.25 27                                                        Halstab 1214                                                                 15 Ferro S1027 0.4 15                                                         16 Ferro S1027 0.25 25                                                         Halstab 1214 0.25                                                          ______________________________________                                    

With reference to the above Table 4, replacement of the primary tin orantimony stabilizer with the coated acid absorber costabilizer providedimproved dynamic stabilities.

Applications were also demonstrated in flexible PVC. Examples 17-21 wereperformed with Halstab 1219 and Halstab 1214, alone, and in combinationwith organotin carboxylates and reverse ester tins. Again, dynamicstabilities were determined at 190° C., 90 rpm for the 65 grams batch onthe following test composition (phr):

    ______________________________________                                        Oxy 220 PVC          100 parts                                                  CaCO.sub.3 10 parts                                                           911 P plasticizer (a blend of straight 45 parts                               chain 9 and 11 crabon phthalates)                                           ______________________________________                                    

With reference to Table 5 for Examples 17-21, improved dynamicstabilities were achieved with good or excellent color hold in the caseof the stabilizer compositions of this invention. Thus, with referenceto Example 21, the effectiveness in flexible PVC with 1-1.5 partscostabilizer with as little as 0.2-0.3 parts tin stabilizer makes thesestabilizer compositions highly cost effective versus mixed metalsystems. Also, in clear semirigid PVC (15 phr plasticizer), excellentdynamic stability is achieved using 0.7 to 1 phr costabilizer plus 0.3to 0.5 phr of a tin maleate, Akcros T878, and the stabilizer system isodorless.

                  TABLE 5                                                         ______________________________________                                        Example                     Failure Time                                                                           Color                                      No. Stabilizer phr (minutes) Hold                                           ______________________________________                                        17      Halstab 1219                                                                              2.5     >60      poor                                       18 Halstab 1214 2.5 >60 poor                                                  19 Halstab 1214 1.25 >60 good                                                  Morton TM694 1.25                                                            20 Halstab 1219 1.25 >60 good                                                  Morton TM694 1.25                                                            21 Halstab 1214 1.25  >120 excellent                                           Akcros T186 0.3                                                            ______________________________________                                    

Examples 22-23 were performed in order to evaluate the inventivestabilizers in highly filled compounds. The following formulation wasused (phr):

    ______________________________________                                        Oxy 220 PVC       100                                                           CaCO.sub.3 100                                                                Clay 200                                                                      Di-isodecyl phthalate  75                                                   ______________________________________                                    

Dynamic stabilities were determined at 190° C., 90 rpm for a 60 gramsbatch. The results are reported in the following table. "Halstab 1218"identifies the costabilizer of hydrotalcite particles coated with 2%dibutyltin oxide and 3% stearic acid.

                  TABLE 6                                                         ______________________________________                                        Example                         Color Hold                                      No. Stabilizer phr (minutes)                                                ______________________________________                                        22        Ba/Zn liquid 2.5      discoloration                                    Mark 4702 (Witco)  after 15-20                                               23 Halstab 1218 1.25 no discoloration                                          Morton TM-694 1.25 after 60                                                ______________________________________                                    

The high efficiency Ba/Zn liquid stabilizer of Example 22 after 15-20minutes at 190° C., 90 rpm for a 75, grams batch. In contrast, the tinstabilizer and costabilizer composition of this invention exhibited nodiscoloration after 60 minutes.

Examples 24-33 were performed to demonstrate various features of thecostabilizers of this invention upon comparison with other stabilizers.Organotin stabilizers were used as the primary stabilizer from severalclasses. The commercial products include Morton TM-181 blends ofdialkyltin bis(iso-thioglycolates) with monoalkyltintris(iso-thioglycolates) which are generally referred to as "tinmercaptides." For comparison, Morton TM-694 is a blend of dialkyltinbis(2-mercaptoethyl oleates) identified above, referred to as "reverseester tins." Ackros T-878M is a dialkyltin carboxylate ester, identifiedabove. These three classes of organotin stabilizers were tested in thefollowing test composition (phr):

    ______________________________________                                        PVC                100                                                          CaCO.sub.3 5                                                                  TiO.sub.2 1                                                                   Calcium Stearate 1.5                                                          Paraffin wax 0.5                                                              Rohm & Haas K334 5                                                            acrylic impact modifier                                                       Rohm & Haas K120N 1                                                           processing aid                                                              ______________________________________                                    

Dynamic stabilities were again determined at 190° C., 60 rpm, for a 65grams batch.

With reference to Table 7, it may be concluded, as is widely known, thatzinc-zeolite costabilizers are effective only with organotin stabilizersof the tin mercaptide type with reference to Examples 24-31. In completecontrast, the new costabilizer of this invention, where the acidabsorber particles of zeolite are coated with a blend of dialkytinoxide, is effective with the reverse ester tins and tin carboxylateesters, as demonstrated by Examples 32-33. Examples 32-33 demonstratedat every stage that the stabilizer compositions of this invention showedless discoloration and extended heat stabilities by comparison withother zinc-zeolite costabilizers.

In Table 7, PQ Corp Valfor 100 is comprised of 90% zeolite and 10% zincstearate and Halstab 1131 is comprised of 90% zeolite and 10% zincstearate. "Halstab 1214" identifies the costabilizer of 95% zeoliteparticles coated with 1.7% dibutyltin oxide and 3.3% stearic acid."Halstab 1215" identifies the costabilizer of 93% zeolite particlescoated with 3% dioctyltin oxide and 4% lauric acid.

                  TABLE 7                                                         ______________________________________                                        Example                        Failure Time                                     No. Stabilizer phr (minutes)                                                ______________________________________                                        24         Morton TM-181                                                                              1.2    35                                               25 Morton TM-181 .6 35                                                         Valfor 100 .6                                                                26 Morton TM-694 2 40                                                          Valfor 100 .6                                                                27 Morton-694 1 18                                                             Halstab 1131 1                                                                Valfor 100 .6                                                                28 Morton TM-694 1 18                                                          Valfor 100 .6                                                                29 Akcros T-878M 2.5 20                                                       30 Akcros T-878M 1.25 12                                                       Halstab 1131 1.25                                                            31 Akcros T-878M 1.25 12                                                      32 Morton TM-694 1 40                                                          Halstab 1214 1                                                                Valfor 100 .6                                                                33 Akcros T-878M 1.25 35                                                       Halstab 1215 1.25                                                          ______________________________________                                    

The costabilizers of this invention are also effective with mixed metalsystems but organo phosphite costabilizers must be omitted because theyreact with dialkyltin oxides or sulfides to form phosphates orthiophosphates. Organosulfur costabilizers such as dilaurylthioproionate (DLTDP) may be used instead of organophosphites in thesesystems.

Having described this invention, its advantages and parameters, it willbe obvious to a person of ordinary skill in the art, in view of theabove description, that variations thereof may be made without departingfrom the spirit and scope thereof.

What is claimed is:
 1. A composition comprising acid absorber particleshaving a coating selected from the group consisting of anorganotin-based coating and a complex calcium/zinc/strontiumphosphate-based coating.
 2. The composition of claim 1 wherein said acidabsorber is selected from the group consisting of zeolite andhydrotalcite.
 3. The composition of claim 1 wherein said organotin-basedcoating contains a fatty acid and an organotin selected from the groupconsisting of a dialkyltin oxide and dialkyltin sulfide.
 4. Thecomposition of claim 3 wherein said fatty acid is selected from thegroup consisting of stearic, oleic, octoic and lauric acids.
 5. Thecomposition of claim 1 wherein said particles are sized in the range ofabout submicron to about 10 microns.